1. Field of the Invention
The invention relates generally to circulating and agitating equipment for pond cultivation, and more particularly, to a circulator and agitator for cultivating algae.
2. Description of Related Art
From time immemorial to the present, humans have cultivated microorganisms—sometimes for processes like fermentation, and sometimes to create a biomass from which nutrients and other valuable chemicals can be extracted. While classic fermentation processes—for example, to produce alcohol or to leaven bread—often rely on simple eukaryotes like S. cerevisiae, over the last few decades, a great deal of attention has been focused on the cultivation of algae.
Algae is a general term for a diverse group of autotrophic, photosynthetic organisms, most of which are aquatic. These organisms may be cultivated for a variety of reasons, and to generate a variety of end products. For example, algae have become an important source of the so-called “omega-3” fatty acids, which are important in human nutrition. Algae are also cultivated to extract their oils, which can be processed into biodiesel and other forms of fuel. Beyond products and byproducts, cultivated algae can also be used in processes like wastewater treatment.
Cultivation of algae can be done in any number of ways, but is typically done in long, shallow ponds of water. Among other things, most cultivation ponds include an agitator or circulator to circulate the water. In a still pond, the water may stratify, with deeper water having less dissolved oxygen than water nearer the surface, and other nutrients and treatments may not reach the entire volume of the pond, leading to uneven algae growth and reduced yield. The agitator or circulator addresses these issues. Additionally, agitation or circulation can ensure that most of the algae get periodic exposure to strong sunlight, as they are brought toward the surface, followed by darker periods as they sink back toward the bottom, a light-dark pattern that has been found by some researchers to be beneficial. Beyond specific effects on algae, water circulation also maintains homogeneity of the water-nutrient mixture, and can help prevent putrefaction and reduce the growth of unwanted, invasive organisms.
For many decades, the paddlewheel has been the typical agitator used in cultivation ponds. An example of this can be found in U.S. Pat. No. 4,217,728 to Shimamatsu et al., a 1980 patent, the contents of which are incorporated by reference in their entirety. While a paddlewheel does provide agitation, it is a point source; it drives the water in the pond from a single location. In order to provide agitation for an entire pond—which may be quite large—paddlewheel agitation both uses and wastes a large amount of energy, and may not provide uniform agitation over the entire volume of the pond.